1. Field of the Invention
The present invention relates to an in-process grinding method which permits dressing during dependent machining, and to a rocking grinding apparatus which is used for grinding and abrading a plane or a spherical surface.
2. Description of the Related Art
FIG. 5 is a cross-sectional view partially showing the major components of a conventional grinding apparatus for a spherical surface during dependent machining.
As shown in FIG. 5, during the dependent machining, an end face, work surface of a workpiece 8 is in contact with the surface of a semi-spherical grinding tool 7 which is rotatably supported with the aid of a rotation shaft 6 connected to a drive source. A holding plate 10, having a plate shape and a pin 9 at its center, is pressed against the workpiece 8. The holding plate 10 tightly contacts the workpiece 8 to hold it. The spherical end of the pin 9 is free to rock. The surface of the workpiece 8 is thus ground to become a smooth spherical surface by the rocking motion caused by the holding plate 10.
Numeral 11 denoted above the grinding tool 7 indicates a coolant (a cooling medium) fed from an outside device through a pipe 12.
The grinding tool 7 is made of an alloy sintered in a heat treatment in which ground powder, such as a diamond powder, and metal power, such as Cu or Sn, are mixed.
In the above-mentioned grinding method, a problem exists in that a grind stone, that is, the grinding tool 7, clogs during grinding, thereby reducing the effectiveness of the grinding performance. As a result, the grinding time required is prolonged. In order to solve the problem, dressing is performed with a dressing tool while the workpiece is being ground.
Although there are forced grinding methods, such as creep-filled grinding or in-filled grinding, other than that mentioned above, a grind stone nevertheless clogs in both of these methods.
In order to solve the above problem, the following methods have been proposed in recent years.
"Grinding mirrors of a glass material with a cast iron fiber bond grinder", Lecture Treatise, Volume 1, Academic Lecture in the Autum Session of Precision Engineering, 1988, by Precision Engineering Corporation Aggregate, Oct. 5, 1988; "Grinding silicones with a cast iron fiber bond grinder", Lecture Treatise, Volume 3, Academic Lecture in the Autum Session of Precision Engineering, 1988, by Precision Engineering Corporation Aggregate, Oct. 5, 1988; and "Grinding electrolytically dressed mirrors of glass with an electrodeposited grinder", Lecture Treatise, Volume 1, Academic Lecture in the Spring Session of Precision Engineering, 1988, by Precision Engineering Corporation Aggregate, Mar. 22, 1989.
The technique discussed in the above-cited documents will be described with reference to FIG. 6, which is a side view showing the principle of the technique.
According to the technique, when a workpiece 34 is interposed to be ground between a grind stone 30 (a cast iron fiber bond diamond grind stone with finely ground powder) and an electrode 33, a weakly charged coolant 32 jets out to enhance in-process dressing effectiveness. At this time, the grind stone 30 becomes a positive electrode by connecting it to an electrolysis dressing power supply 36 through a charge-feeding brush 35, and the electrode 33, which is disposed between the grind stone 30 and a rotary table 31 opposite to the grind stone 30, becomes a negative electrode by connecting the electrode 33 to the electrolysis dressing power supply 36. With this arrangement, dressing can be performed during grinding. A coolant 37 for grinding is fed through the inside of the grind stone 30. The grind stone 30 and the rotary table 31 rotate respectively in the directions indicated by arrows in FIG. 6.
According to this method, the position of the grind stone (shaft) 30 and that of the negative electrode 33 are always fixed, and the negative electrode 33 and the grinding face of the grinding stone 30 are maintained with a fixed space therebetween. Further, grinding is performed so that the workpiece 40 and the negative electrode 33 above the rotary table 31 do not interfere with each other.
In such dependent machining as described above, as shown in FIG. 5, the periphery point L of the workpiece 8 rocks between the points I and O of the spherical surface associated with the grinding tool 7. In this case, the portion of the spherical surface of the grinding tool 7 between a point O and a periphery point e is where the workpiece 8 and the grinding tool 7 do not interfere with each other on the spherical surface of the grinding tool 7.
The grinding tool 7 is made to become a positive electrode, while on the contrary, the surface between the points O and e is made to become a negative electrode. When a weakly charged coolant is fed to the surface between the two points, the surface is electrolytically in-process dressed.
When the grinding tool 7 grinds on the spherical surface of the grinding tool 7 between a point C to which the axis of the rotation shaft 6 extends and the point e, however, there is a disadvantage in that the surface between the two points O and e is dressed, whereas the surface between the two points C and O is not dressed. That is, since the surface between the two points C and O is within the rocking range of the grinding tool 7, the grinding tool 7 cannot cover its rocking range if the negative electrode is fixed.